1. Field of the Invention
The present invention relates to material analysis.
2. Discussion of Prior Art
Known methods of material analysis include using an intensity modulated ultrasonic source to measure material properties. In such prior art systems, a single ultrasonic probe operating at a single frequency is aimed towards a sample of a material. The resulting vibrations through the sample are measured in order to obtain data about the sample.
The known ultrasonic material analysis apparatus uses only one ultrasonic transducer operating at a single frequency with an amplitude modulated by a second frequency and using intensity detectors to obtain a reading of ultrasonic absorption. However, this approach results in standing waves being set up in the sample under inspection and generating hot spots. These hot spots are indistinguishable from damaged areas and so often result in misidentification of damage within the sample. This approach also has the disadvantage that readings can only be obtained for the overall probed area and does not allow finer analysis of sub-regions within the area.
It is also known to use lock-in thermography techniques to analyse materials. This involves aiming a halogen lamp at a sample and modulating the intensity sinusoidally with a known frequency. An infra-red camera then captures a thermal image of a surface of the sample at the modulated frequency.
Whilst these prior art techniques can be useful for several types of material analysis, they are limited in usefulness for detecting barely visible impact damage (BVID) which exhibit areas of shattered material.
An object of the present invention is to provide a material analysis technique which can produce improved results in detecting BVID and other material characteristics.
According to a first aspect of the present invention there is provided apparatus for material analysis including:
means for directing vibrational energy into a material sample in sufficient quantity to generate heat in the sample; and
means for capturing a thermal image of the sample.
Preferably, the thermal imaging is adapted to detect heat emitted from a damage site in the sample. The means for directing vibrational energy into the sample preferably generates vibrations in the frequency range 10 Hz to 1 MHz, and more preferably in the ultrasonic frequency range.
Preferably, the ultrasonic energy emitting means includes two ultrasonic probes for being attached to the sample. Preferably, the two probes in use emit sonic energy at different respective frequencies. Preferably, the apparatus includes means for modulating the intensity of the sonic energy emitted by each of the probes.
In a preferred embodiment, one of the two probes operates at a frequency of approximately 35 kHz and the other operates at a frequency of approximately 40 kHz. Preferably, the modulating means modulates the intensities of the two probes xcfx81/2 out of phase with each other. The modulation frequency may be between 0.01 and 2.0 Hz.
The means for capturing the thermal image may be configured to sample at an integer multiple of the modulation frequency, preferably at approximately twice the modulation frequency.
The means for capturing the thermal image preferably includes an infra-red camera.
According to a second aspect of the present invention there is provided a method of material analysis including steps of:
directing vibrational energy into a material sample; and
capturing a thermal image of the sample.
Preferably, the step of directing vibrational energy into the sample includes attaching two probes to the sample, the probes being configured to operate at two different respective frequencies. Preferably, the intensities of the two probes are modulated out of phase with each other.
Whilst the invention has been described above it extends to any inventive combination of features set out above or in the following description.